An Operating System (OS) is a software program that controls physical computer hardware (e.g., a processor, memory, and disk and CD-ROM drives) and presents application programs with a unified set of abstract services (e.g., a file system). Modern OSs typically multi-task among several application programs, each of which executes in a separate process, and many enable application programs to multi-task among several “threads” that share the same process address space.
Modern processors frequently have “performance counters,” software-configurable registers that count occurrences of various performance “events.” Typical events include “instructions retired” and “processor cycles,” the ratio of which is the well-known metric Instructions Per Clock (IPC), as well as various types of cache misses. Performance monitoring applications use these counters and events to evaluate and tune the performance of other applications. In a multi-tasking environment, performance monitoring applications must distinguish events such as cache misses that occur in one program or thread from those that occur in other programs or threads. Since hardware counters count these events, the inability to track OS process and thread execution in hardware limits the usefulness of the performance monitoring applications.
A Virtual Machine Monitor (VMM) is a software program that controls physical computer hardware (e.g., a processor, memory, and disk and CD-ROM drives) and presents programs executing within a Virtual Machine (VM) with the illusion that they are executing on real physical computer hardware (a “bare” machine, e.g., a processor, memory and a disk drive). Each VM typically functions as a self-contained platform, controlled by a “guest” OS (i.e., an OS hosted by the VMM), which executes as if it were running on a “bare” machine instead of within a virtual machine. Recursive VMs are VMs that are controlled by a VMM that is itself executing within a VM.
In a “real-time” application, computations upon data that is available at one substantially predetermined time should be completed by another substantially predetermined time. If an OS (or VMM) schedules a thread or process (or VM) with sufficient frequency and for sufficient duration that the thread or process (or VM) is able to complete its computations before their respective deadlines, the thread or process (or VM) is said to have received adequate scheduling Quality of Service (QoS). OSs and VMMs should schedule the computing resources of their real or virtual machine in such a fashion as to ensure that real-time applications receive adequate scheduling QoS.
A VMM can monitor scheduling QoS at the level of all applications within a VM as disclosed in the related application Ser. No. 09/541,444. However, such monitoring cannot distinguish between real-time and non-real-time applications in the same VM, nor can it distinguish among recursive VMs in the same VM, leading to problems in providing adequate scheduling QoS. Furthermore, a system wide performance monitoring facility that executes as part of a VMM will need to distinguish events in one VM from those in another VM.